Method of producing semiconductor device

ABSTRACT

A method of producing semiconductor device for reducing a gas of halogenated product of a group IVa element with H 2  by the ECR plasma CVD method to form a thin film of the group IVa element on a substrate is disclosed. This method includes forming an adhesion layer of the group IVa element in a contact hole including walls, to be in contact with the exposed substrate, the adhesion layer being formed by reducing with H 2  a gas of halogenated product of the group IVa element in an ECR plasma CVD process, the group IVa element and H 2  being used at a flow ratio of 0.4 and greater; forming a barrier layer in contact with the adhesion layer; and filling the contact hole with an electrically conductive material. The stable barrier metal is formed and an upper-layer metallization material is filled within the minute contact hole having a large aspect ratio.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method of metallization of asemiconductor device, and particularly to a method of producing a highlyreliable contact part, which is adapted for improving conformality of athin film of a group IVa element, above all a Ti film employed as abarrier metal, by the electron cyclotron resonance (ECR) plasma CVDmethod.

[0003] 2. Description of the Related Art

[0004] For filling a metallization material into a contact hole ofrecent VLSI or ULSI, particularly a contact hole for havingsubstrate-contact with an impurity diffused region in an Si substrate,aluminum (Al) and tungsten (W) are broadly used as an electricallyconductive material for filling.

[0005] In order to enhance the reliability of contact by these fillingmetals, the inner wall of the contact hole is covered with a barriermetal composed of the group IVa element before the filling. A barriermetal which has a two-layer structure consisting of a titanium (Ti) filmand a titanium nitride (TiN) film is employed as the above-mentionedbarrier metal. The barrier metal of two-layer structure is employed forproviding a Ti film having capability of reducing a natural oxidationfilm on the substrate of the Si substrate so as to assure ohmicproperty, and for stacking a TiN film thereon to assure barrierproperty.

[0006] These Ti film and TiN film are formed generally by sputtering.The process of forming the latter TiN film is particularly calledreactive sputtering, in which a Ti target is sputtered in anitrogen-containing atmosphere.

[0007] However, with the sputtering method, the step coverage in arecent contact hole of high aspect ratio is insufficient. Grains of afilm forming material sputtered out from the target are incident on thesubstrate with certain directionality. Therefore, the travelling grainsare prevented from reaching deep inside of the hole by shadowing effectof the sidewalls of the contact hole itself.

[0008] Thus, the CVD method is expected to be promising as it is capableof forming the barrier metal with satisfactory coverage on the basis ofchemical reactions of the surface in the contact hole.

[0009] The TiN film can be formed relatively easily by a known processusing various material gases and the CVD method. For instance, anexample of forming the TiN film based on methylhydrazine reduction ofTiCl₄ using a low pressure CVD device of parallel flat platesingle-wafer processing is reported in Monthly Semiconductor World,January 1993, pages 145-151. The formation Gibbs energy in this reactionsystem of TiN at normal temperatures is approximately −209 kJ/mol(ΔG<0). The system is thermodynamically stable.

[0010] On the contrary, the reaction system of film formation of the Tifilm by the CVD method is limited to H₂ reduction of TiCl₄ as far as itis known. In addition, the forming Gibbs energy in the reaction systemas shown by the following formula is 209 kJ/mol (ΔG>0), which is veryhigh, at temperatures within a range of 100 to 1000° C. for currentlypractical semiconductor processes.

TiCl₄+2H₂→Ti+4HCl

[0011] Therefore, film formation of the Ti film by the conventional CVDmethod has rarely been realized.

[0012] Recently, a technique of forming the Ti film by the ECR plasmaCVD method utilizing ECR discharge of high dissociation efficiency ofmaterial gases has been proposed instead of the conventional heat CVDmethod.

[0013] However, the Ti film formation by this method is not satisfactoryin reliability and reproducibility. For instance, if the Ti film growsinto grains, not conformal, under certain conditions, the TiN filmgrowing thereon inherits the surface profile of the Ti film, thusfurther increasing surface irregularities of the barrier metal.Consequently, problems arise, such as, generation of a crack in a cornerpart on the bottom of the contact hole, and difficulty in filling thecontact hole with an upper-layer metallization material in the latterprocess. The Ti film is a critical component for assuring the ohmicproperty of the contact. The conformality of the Ti film is arequirement for assuring reliability of the contact part.

OBJECT AND SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to provide a method ofproducing semiconductor device which is adapted for improvingconformality of the Ti film formed by the ECR plasma CVD method and forraising reliability of the contact part.

[0015] According to the present invention, there is provided a method ofproducing semiconductor device including the steps of: forming aninsulating layer on a substrate; forming a contact hole in theinsulating layer to expose a selected portion of the substrate, thecontact hole being defined by walls of the insulating layer; forming anadhesion layer of a group IVa element in the contact hole including thewalls, to be in contact with the exposed substrate, the adhesion layerbeing formed by reducing with H₂ a gas of halogenated product of thegroup IVa element in an ECR plasma CVD process, the group IVa elementand H₂ being used at a flow ratio of 0.4 and greater; forming a barrierlayer in contact with the adhesion layer; and filling the contact holewith an electrically conductive material.

[0016] If the flow ratio of the group IVa element to H₂ is smaller than0.4, grain growth of Ti is observed in a fine contact hole. Although theupper limit of the flow ratio is not particularly defined, anexcessively large flow ratio may lower the reduction capability of H₂,disturbing achievement of practical film forming speed. Therefore, theflow ratio is selected in a range approximately up to 2.

[0017] After a thin film of the group IVa element is formed, a nitridefilm of the group IVa element may be continuously formed on the thinfilm.

[0018] The nitride film may be formed by the CVD method or in aself-aligned manner by annealing the thin-film of the group IVa elementin a nitrogen-containing atmosphere.

[0019] The group IVa element includes three types, that is, Ti,zirconium (Zr) and hafnium (Hf). Forming the Ti film using a TiCl₄ gasis particularly effective.

[0020] In an experiment, when the flow ratio of a TiCl/H₂ mixed gas wasset to 0.4 or greater, conformal formation of the Ti film was possible.On the contrary, at a flow ratio of the TiCl/H₂ mixed gas of 0.4 orsmaller, grain growth of Ti was observed. The reason for the aboveresults is conceivably as follows. As an excessive amount ofby-products, such as HCl, are generated near the bottom of the finecontact hole in the atmosphere containing an excessive amount of H₂,vapor pressures in a micro ambient is lowered and release thereof isrestricted. Consequently, individual Ti crystalline nuclei growextraordinarily. From the above phenomenon, it is conceivable that thequantity balance of the by-products from the viewpoint of the vaporpressure can be improved at the flow ratio of 0.4 and greater, and thatother Ti crystalline nuclei are sequentially formed on the substratebefore the individual crystalline nuclei grow extraordinarily, thusrealizing conformality.

[0021] As the Ti film is thus formed conformally, even when a TiN filmis stacked on the Ti film by the CVD method, a film inheriting theproperty of the underlying film can be grown. Thus, the risk ofgenerating the crack in the corner part of the contact hole iseliminated.

[0022] If the Ti film is annealed in a nitrogen-containing atmosphere,the TiN film is formed conformally and in a self-aligned manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIGS. 1A to 1D are cross-sectional views of an example of a seriesof processes, sequentially shown, in which the method of the presentinvention is applied to filling a contact hole. FIG. 1A shows a state inwhich the contact hole is closed with an SiO₂ interlayer insulatingfilm. FIG. 1B shows a state in which a Ti film is formed conformally bythe ECR plasma CVD method. FIG. 1C shows a state in which a TiN film isformed conformally. FIG. 1D shows a state in which the contact hole isuniformly filled with an upper-layer metallization film.

[0024]FIGS. 2A to 2C are cross-sectional views of another example of aseries of processes, sequentially shown, in which the method of thepresent invention is applied to filling the contact hole. FIG. 2A showsa state in which a conformal Ti film is formed to cover the contacthole. FIG. 2B shows a state in which a conformal TiN film and a TiSi₂layer are formed in a self-aligned manner by nitriding anneal. FIG. 2Cshows a state in which the contact hole is uniformly filled with anupper-layer metallization film.

[0025]FIGS. 3A and 3B are cross-sectional views of a comparative exampleof filling the contact hole, sequentially shown. FIG. 3A shows a statein which a granular Ti film has grown within the contact hole. FIG. 3Bshows a state in which a TiN film having large surface irregularitieshas grown on the Ti film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Preferred embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings.

EXAMPLE 1

[0027] The present example is of the contact hole filling process. Inthis example, a Ti film was formed by the ECR plasma CVD method at aTiCl₄/H₂ flow ratio of 0.8, and then a TiN film was continuously formedsimilarly by the ECR plasma CVD method. Finally, the contact hole wasfilled with a Al-1% Si film. This process will be explained withreference to FIGS. 1A to 1D.

[0028] A sample wafer used in this example has a contact hole 3 with adiameter of approximately 0.3 μm opened in an SiO₂ interlayer insulatingfilm 2 with a thickness of approximately 1 μm deposited on an Sisubstrate 1, as shown in FIG. 1A. Therefore, the contact hole 3 exhibitsan aspect ratio of 3 or greater. However, the aspect ratio is expressedin a compressed manner in FIGS. 1A to 1D.

[0029] The wafer was set on an ECR plasma CVD device, and a Ti film witha thickness of 2 to 10 nm was formed under the following conditions.TiCl₄ flow rate 24 SCCM H₂ flow rate 30 SCCM gas pressure 0.12 Pamicrowave power 2.8 kW (2.45 GHz) film forming temperature 420° C.

[0030] By setting the above conditions, a Ti film 4 c for conformallycovering the inner wall surface of the contact hole was formed, as shownin FIG. 1B. The subscript “c” indicates conformality hereinbelow.

[0031] Next, a TiN film was continuously formed in the same device.Exemplary film forming conditions are shown as follows. TiCl₄ flow rate20 SCCM H₂ flow rate 26 SCCM N₂ flow rate 6 SCCM gas pressure 0.23 Pamicrowave power 2.8 kW (2.45 GHz) film forming temperature 420° C.

[0032] In this process, a TiN film 5 c reflecting the profile of theconformal underlying Ti film 4 c and being similarly conformal wasformed, as shown in FIG. 1C. Cracks and defects at the corner part ofthe bottom of the contact hole 3 were not observed.

[0033] The contact hole 3 thus having a satisfactory barrier metalformed thereto was uniformly filled with an upper-layer metallizationfilm 6, as shown in FIG. 1D. As the upper-layer metallization film 6 inthis example, an Al-1% Si film formed by high-temperature sputtering ora tungsten (W) film formed by the blanket CVD method can be used. Ineither case, satisfactory results were obtained.

EXAMPLE 2

[0034] In the present example, a Ti film was conformally formed, andthen the Ti film was annealed in a nitrogen-containing atmosphere toform a TiN film in a self-aligned manner. This process will be describedwith reference to FIGS. 2A to 2C. Reference numerals of FIGS. 2A to 2Care partly the same as those of FIGS. 1A to 1D.

[0035] First, a wafer as shown in FIG. 2A, having a TiN film 4 c formedthereon in a manner similar to Example 1, was set on an annealing deviceand was nitrided at annealing temperatures of 500 to 900° C. forannealing time of 30 to 120 seconds in an N₂ atmosphere or an ammonium(NH₃) atmosphere.

[0036] By this nitriding anneal, the Ti film 4 c was changed into a TiNfilm 7 c on an SiO₂ interlayer insulating film 2, as shown in FIG. 2B.

[0037] A major part of the Ti film 4 c was changed into the TiN film 7 con the bottom of the contact hole 3, and a titanium/silicide (TiSi₂)layer 8 was formed in a self-aligned manner on the boundary face withthe Si substrate 1. This TiN/TiSi₂ two-layer structure was generated forthe following reasons. Since TiN having a formation Gibbs energy of−336.6 kJ/mol is thermodynamically more stable than TiSi₂ having aformation Gibbs energy of −134.4 kJ/mol, the nitriding of the Ti film onthe bottom of the contact hole 3 precedes the silicification thereof,and the resulting TiN film 7 c serves as a barrier to external diffusionof Si. By this process, formation of the barrier metal and ohmic contactwere simultaneously achieved.

[0038] On the TiN film 7 c which was conformally formed, the contacthole 3 was stably filled with the upper-layer metallization film 6, asshown in FIG. 2C. Thus, low-resistance contact was realized.

COMPARATIVE EXAMPLE

[0039] In the present comparative example, a Ti film was formed at aTiCl₄/H₂ flow rate of 0.2, and a TiN film was subsequently formedthereon. This process will be explained with reference to FIGS. 3A and3B.

[0040] First, the wafer as previously shown in FIG. 1A was set on an ECRplasma CVD device, and a Ti film with a thickness of 2 to 10 nm wasformed under the following conditions. TiCl₄ flow rate 6 SCCM H₂ flowrate 30 SCCM gas pressure 0.12 Pa microwave power 2.8 kW (2.45 GHz) filmforming temperature 420° C.

[0041] Under the above conditions, a conformal Ti film 4 c was formed inthe extreme vicinity of the upper surface of the SiO₂ interlayerinsulating film 2 the opening end of the contact hole 3, as shown inFIG. 3A. However, a granular Ti film 4 g grew on the sidewall surface tothe bottom. The subscript “g” indicates that the Ti film is granular.The above phenomenon is generated conceivably because an excessiveamount of H₂ in the film forming gas prevents reaction by-products frombeing released, causing Ti crystal nuclei to grow extraordinarily.

[0042] If a TiN film was subsequently formed thereon by the ECR plasmaCVD method, a conformal TiN film 5 c grew on the conformal Ti film 4 c,as shown in FIG. 3B. However, a granular TiN film 5 g grew on thegranular Ti film 4 g, intensifying the surface irregularities. Also, acrack was generated in the corner part on the bottom of the contact hole3.

[0043] The upper-layer metallization film, not shown, was not filleduniformly on such a non-uniform barrier metal, and sufficient ohmiccontact was not achieved. Also, a leak current was increased by thecrack.

[0044] The present invention is described above on the basis of the twoexamples. However, it is to be understood that the present invention isnot limited to these examples, and that details of the structure of thesample wafer and the film forming conditions may be suitably modified.

[0045] For instance, the structure of the barrier metal is not limitedto the above-described Ti/TiN two-layer structure. A Ti/TiN/Tithree-layer structure having another Ti film stacked on the two-layerstructure may also be employed.

[0046] In the above embodiment, the contact hole filling process isexplained. A similar filling process is effective for a via hole.

[0047] As is clear from the above description, according to the presentinvention, a conformal Ti film can be formed stably by the ECR plasmaCVD method. Thus, a barrier metal can be stably formed and anupper-layer metallization material can be filled even within a finecontact hole having a large aspect ratio. Consequently, a semiconductordevice having highly reliable metallization can be produced.

What is claimed is:
 1. A method of producing semiconductor devicecomprising the steps of: forming an insulating layer on a substrate;forming a contact hole in the insulating layer to expose a selectedportion of the substrate, the contact hole being defined by walls of theinsulating layer; forming an adhesion layer of a group IVa element inthe contact hole including the walls, to be in contact with the exposedsubstrate, the adhesion layer being formed by reducing with H₂ a gas ofhalogenated product of the group IVa element in an ECR plasma CVDprocess, the group IVa element and H₂ being used at a flow ratio of 0.4and greater; forming a barrier layer in contact with the adhesion layer;and filling the contact hole with an electrically conductive material.2. The method of producing semiconductor device as claimed in claim 1,wherein the barrier layer is composed of nitride of the group IVaelement.
 3. The method of producing semiconductor device as claimed inclaim 2, wherein the nitride of the group IVa element is formed into afilm continuously on the adhesion layer.
 4. The method of producingsemiconductor device as claimed in claim 3, wherein the nitride of thegroup IVa element is deposited by a CVD process.
 5. The method ofproducing semiconductor device as claimed in claim 2, wherein thenitride of the group IVa element is formed in a self-aligned manner byannealing the barrier layer of the group IVa element in anitrogen-containing atmosphere.
 6. The method of producing semiconductordevice as claimed in claim 1, wherein the group IVa element is Ti andthe gas of halogenated product is TiCl₄.